Placement aptitude gives ~75 seconds per question. These shortcuts turn 2-minute problems into 20-second ones.
Percentages — memorize the fraction map
1/8=12.5% · 1/6=16.66% · 1/5=20% · 1/4=25% · 1/3=33.3% · 3/8=37.5%. "37.5% of 640" → 3/8 × 640 = 240. No calculator thinking.
Successive change formula
Two changes a% then b%: net = a + b + ab/100. Price +20% then −10% → 20−10−2 = +8%. Works for discounts, populations, areas.
Time & Work — the LCM method
A does a job in 12 days, B in 8. Take LCM(12,8)=24 units total. A does 2/day, B does 3/day → together 5/day → 24/5 = 4.8 days. No fractions-of-fractions mess.
Profit/Loss anchors
- CP with successive profit: SP = CP × 1.2 × 0.9 style multiplication
- Dishonest seller using false weight w: profit% = (1000−w)/w × 100
Where marks actually are
Frequency order in TCS/Infosys/Cognizant tests: percentages > time-work > ratios > averages > series > P&L. Master the first four before touching probability. Practice sets: IndiaBix topic-wise, then timed mocks.